Pressure vessels and method of fabrication

ABSTRACT

A pressure vessel includes curved sidewalls configured as a frame having a polygonal outline, a planar top side and a planar bottom side attached to the curved sidewalls forming a sealed pressure chamber therebetween. Each planar side includes a contoured surface having shaped pressure resistant features formed thereon. A preferred method for forming the pressure resistant features includes hydraulic pressurization to induce plastic strain. The pressure vessel also includes an array of internal support posts within the sealed pressure chamber attached to the planar sides in a geometrical pattern, such as a hexagonal array. The support posts can be solid metal cylinders, hollow tubes or tubes through which reinforcing materials, such as carbon fiber, glass fiber, or fiber/epoxy tape have been passed. A composite pressure vessel includes tubular internal support posts reinforced with reinforcing materials, as well as contoured surfaces and curved sidewalls reinforced with these same reinforcing materials.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority from U.S. Provisional No. 62/830,700,filed Apr. 8, 2019, which is incorporated herein by reference.

FIELD

This disclosure relates to pressure vessels and to methods forfabricating pressure vessels.

BACKGROUND

Conventional pressure vessels have cylindrical or spherical shapesbecause radiused surfaces effectively resist internal pressure forces.FIG. 1A illustrates a prior art cylindrical pressure vessel 10C. FIG. 1Billustrates a prior art spherical pressure vessel 10S. One problem withthese shapes is that rectilinear “box” space is not filled efficientlyby cylinders or spheres. As shown in FIG. 1A, the cylindrical pressurevessel 10C has a box space 12C. As shown in FIG. 1B, the sphericalpressure vessel 10S (FIG. 1B) has a box space 12S. A cylinder fills 79%(π/4) and a sphere 52% (π/6) of rectilinear boxes around them,calculated as follows: (Cylinder Volume=πR²L, Box Volume=4R²L, VolumeUsed=π/4=79%) (Sphere Volume=4/3 πR³, Box Volume=8R³, VolumeUsed=π/6=52%).

Space inside vehicles is measured in rectilinear units, (e.g., cubicmeters). However, as demonstrated above rectilinear “box” space is notfilled efficiently by cylinders or spheres. Prior art attempts tofabricate box shaped pressure vessels have not been effective becausetruly flat surfaces, such as rectangular boxes, cannot resist pressurewithout bowing.

The present disclosure is directed to pressure vessels having planarsurfaces and polygonal outlines that efficiently fill available spacesin volume-limited systems, such as motor vehicles or personal breathingsystems (scuba, medical oxygen, etc.). In addition, the pressure vesselshave an internal construction configured to resist pressure withoutdeformation.

SUMMARY

A pressure vessel includes curved sidewalls configured as a frame havinga polygonal outline, and opposing planar sides including a planar topside and a planar bottom side attached to the curved sidewalls forming asealed pressure chamber therebetween. Each planar side includes acontoured surface having shaped pressure resistant features formedthereon. Exemplary pressure resistant features include dome features andsaddle features formed in the contoured surfaces with complextransitions therebetween. In addition, the pressure resistant featuresare formed with small radius contours to resist pressure forces in thesealed pressure chamber, while minimally affecting the substantiallyplanar characteristics of the planar sides of the pressure vessel. Apreferred method for forming the pressure resistant features can includehydraulic pressurization by applying a pressure to the sealed pressurechamber that is much higher than an intended service pressure of thepressure vessel to induce plastic strain.

The pressure vessel also includes an array of internal support postswithin the sealed pressure chamber attached to the planar sides in ageometrical pattern, such as a hexagonal array. The support posts can besolid metal cylinders, hollow tubes or tubes through which reinforcingfibers, such as carbon fibers, glass fibers, or fiber/epoxy tape havebeen passed. The support posts provide structural rigidity andcompressive strength for the pressure vessel and prevent bowing of theplanar sides. With the support posts arranged in a hexagonal array, theweight and volume needed to resist any given internal pressure in thesealed pressure chamber can be minimized. The pressure vessel can alsoinclude welded or brazed joints between the internal support posts andthe planar sides configured to resist shear stresses and prevent leakageor permeation of gases from the sealed pressure chamber.

An exemplary material for the pressure vessel comprises a weldable orbrazable metal, such as stainless steel, aluminum or a high temperaturemetal alloy, such as a titanium or nickel alloy. The pressure vessel canbe configured to contain a variety of fluids and gases includinghydrogen and hydrogen compounds.

The pressure vessel can be used as a metal liner for a compositepressure vessel constructed of composite materials for increasedstrength. A composite pressure vessel can include tubular internalsupport posts reinforced with reinforcing materials, such as carbonfibers, glass fibers, fiber/epoxy tape and cured fiber/epoxy materials.The composite pressure vessel can also include contoured surfaces andcurved sidewalls reinforced with these same materials.

A method for fabricating a pressure vessel includes the steps of:forming a frame having curved sidewalls in a polygonal outline, formingopposing planar sides, forming an array of internal support postsattached to the planar sides in a selected geometrical pattern;attaching the planar sides to the frame to form a sealed pressurechamber by forming a plurality of welded or brazed joints between theinternal support posts and the planar sides configured to resist shearstresses and prevent leakage or permeation of gases from the sealedpressure chamber; and forming contoured surfaces with integral shapedpressure resistant features on the planar sides. A preferred method offorming the shaped pressure resistant features on the planar sidescomprises in situ hydraulic pressurization of the pressure vessel byapplying a forming pressure that is much higher than the intendedworking pressure of the pressure vessel.

A method of fabricating a composite pressure vessel can include the stepof providing the pressure vessel using the previous steps, except forthe forming of the shaped pressure resistant features. Reinforcingmaterials, such as carbon fibers, glass fibers and/or fiber/epoxy tapecan then be loosely applied over selected surfaces of the pressurevessel and through tubular internal support posts, leaving apredetermined amount of slack to accommodate growth during hydraulicpressurization. The internal pressure vessel can then be hydraulicallyinflated to form the contoured surfaces and apply tension to thereinforcing materials. The amount of slack and the hydraulic pressurelevel can be adjusted to induce prestress or “autofrettage”. Curing ofthe resins in the reinforcing materials follows the forming/tensioningstep. The pressure vessel can also be provided with a polygonal outlinethat facilitates applying of the reinforcing materials. For example,corners of the polygonal outline of the pressure vessel can be parallelto a row of internal support posts of the hexagonal array.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a perspective drawing of a prior art cylindrical pressurevessel illustrating its box space;

FIG. 1B is a perspective drawing of a prior art spherical pressurevessel illustrating its box space;

FIG. 2 is a perspective drawing of a pressure vessel having curvedsidewalls, opposing planar sides and internal support posts illustratingan enlarged portion of a planar side;

FIG. 3A is an enlarged cross sectional view taken along section line3A-3A of FIG. 2 illustrating a shaped pressure resistant feature;

FIG. 3B is an enlarged cross sectional view taken along section line3B-3B of FIG. 2 illustrating shaped pressure resistant features;

FIG. 4 is a schematic drawing illustrating internal support posts in aselected geometrical array;

FIG. 5A is a perspective drawing illustrating a frame forming step in amethod for fabricating the pressure vessel;

FIG. 5B is a photograph illustrating the complex shaped pressureresistant features forming step in the method for fabricating thepressure vessel;

FIG. 5C is a schematic drawing illustrating an internal post formingstep in the method for fabricating the pressure vessel;

FIG. 5D is a schematic drawing illustrating an attaching of the planarsides to the frame step in the method for fabricating the pressurevessel;

FIG. 6 is a perspective drawing of a composite pressure vessel;

FIG. 7 is a schematic drawing illustrating the fabrication of reinforcedinternal support posts of the composite pressure vessel with radialsymmetrical wrapping of contoured surfaces;

FIG. 8 is a schematic drawing illustrating the fabrication of reinforcedcurved sidewalls of the composite pressure vessel;

FIG. 9 is a perspective drawing illustrating the fabrication ofreinforced internal support posts of the composite pressure vessel andwrapping of the reinforced sidewalls;

FIG. 10 is a schematic plan drawing of a composite pressure vesselhaving corners that are parallel to a row of tubular internal supportposts in a hexagonal array to facilitate application of reinforcingmaterials;

FIG. 11 is a schematic drawing illustrating a stress analysis ofcomposite internal support posts having reinforcing material therein;and

FIG. 12 is a perspective drawing of the pressure vessel (or thecomposite pressure vessel) illustrating dimensions for calculating thebox space occupied by the pressure vessel.

DETAILED DESCRIPTION

Referring to FIG. 2, a pressure vessel 14 includes four curved metalsidewalls 16 configured as a frame 18 (FIG. 5A) having a polygonaloutline. The pressure vessel 14 has an exterior outline that matches thepolygonal outline of the frame 18. As used herein, the term polygonaloutline means a closed shape with three or more straight sides. In theillustrative embodiment the polygonal outline comprises a square. Other,exemplary polygonal outlines include rectangle, triangle, hexagon, andoctagon. As also shown in FIG. 2, the curved metal sidewalls 16 can havea half pipe shape. Other exemplary shapes can include quarter pipe shapeand three quarter pipe shape.

The pressure vessel 14 also includes two opposing planar sides in theform of a planar top side 20T and a planar bottom side 20B. The planartop side 20T and the planar bottom side 20B are parallel to one anotherand are attached to the curved sidewalls 16 by continuous welded orbrazed joints 22. The curved sidewalls 16 and the planar sides 20T, 20Bform a sealed pressure chamber 26. The pressure vessel 14 also includesan array of internal support posts 24 within the sealed pressure chamber26 attached to the planar sides 20T, 20B in a selected geometricalpattern using welded or brazed joints 22SP. The welded or brazed joints22SP are designed to resist shear stresses and prevent leakage orpermeation of gases out of the pressure vessel 14. In the illustrativeembodiment, the internal support posts 24 are welded or brazed tointernal surfaces of the planar sides 20T, 20B in hexagonal arrays 28,with each internal support post 24 perpendicular to the planar sides20T, 20B. With this arrangement, the planar top side 20T and the planarbottom side 20B are parallel to one another. However in otherembodiments, planar sides can be oriented at different angles withrespect to one another (e.g., 90 degrees). In addition, although onlytwo planar sides 20T, 20B are illustrated, there can be more, but onlyin opposing pairs of sides with internal support posts 24 between them.

In FIG. 2, for illustrative purposes, the area occupied by a singlehexagonal array 28 has been enlarged and separated from the pressurevessel 14. The hexagonal array 28 is shown in more detail in FIG. 4. Theinternal support posts 24 can be placed in the hexagonal array 28 tominimize their displacement of pressure vessel internal volume and alsotheir mass. In addition, the radial symmetry of the hexagonal array 28minimizes the radii of the saddle features 38S and the dome features 38Don the planar sides 20T, 20B. As will be further explained, radialsymmetry also gives an optimal arrangement for reinforcing fibers in acomposite version of the pressure vessel 14. The internal support posts24 also provide significant compressive strength for the pressure vessel14. This simplifies handling during manufacture of the pressure vessel14 and resists stresses from vehicle mounting brackets or accidentalimpact during use of the pressure vessel 14.

As shown in FIG. 2, the planar top side 20T includes a contoured surface36 having a pattern of shaped pressure resistant features 38. In theillustrative embodiment the pressure resistant features 38 includesaddle features 38S (FIG. 3A) and dome features 38D (FIG. 3B). As shownin FIG. 3A, the saddle features 38S bow outwardly from the planar topside 20T and from the sealed pressure chamber 26 with a radius of R anda generally convex shape when viewed from the sealed pressure chamber26. As shown in FIG. 3B, the dome features 38D each include two domes42D that bow outwardly from the planar top side 20T and from the sealedpressure chamber 26 with a radius of R and a saddle point 40D. Asymmetrical way to look at each dome 42D is as surrounded by threesaddle points 40D and three internal support posts 24. The sectionalview in FIG. 3B coincidentally shows two domes 42D at 90 degrees from asaddle point 40D, such that the contoured surface 36 comprises ahexagonal array of individual domes 42D (FIG. 3B).

Referring to FIG. 3A, an exemplary geometry for the saddle features 38Sis illustrated. In this example, the internal support posts 24 comprisesolid or hollow metal cylinders having a diameter D of 0.25″, a centerline CL spacing S of 1″ and a variable length L. In addition, the planartop side 20T has a thickness t of 0.035″. Further, the saddle point 40Shas a radius R of 0.70″ with a maximum height on the planar top side 20Tlocated midway between the internal support posts 24. The planar bottomside 20B (FIG. 2) can have the same saddle features 38S with the samegeometry.

Referring to FIG. 3B, an exemplary geometry for the dome features 38D isillustrated. In this example, the internal support posts 24 comprisesolid or hollow metal cylinders having a diameter D of 0.25″, a centerline CL spacing S of 1″ and a variable length L. In addition, the planartop side 20T has a thickness t of 0.035″. Further, two equally spaceddomes 42D having a radius R of 1.10″ and a saddle point 40D midwaybetween the internal support posts 24 are formed.

In FIGS. 3A and 3B, the planar top side 20T and the contoured surface 36can be formed using plastic strain by applying a pressure much higherthan the intended service pressure. For example, the planar top side 20Tcan be hydraulically formed at 2000 psi during the manufacture of apressure vessel intended for 1 k psi service. Relaxation afterplastically forming the desired shape induces autofrettage. Thisimproves durability and crack resistance of the pressure vessel 14.

Example. A primary objective of this exemplary design is to reduce hoopstress in the planar top side 20T (FIG. 2) and the planar bottom side20B (FIG. 2) by shortening the radii of curvature. Hoop stress is auseful approximation for analysis of thin-walled pressure vessels.Wikipedia.org (ref) defines hoop stress, σ, as follows:σ_(sphere)=PR/2t, σ_(cylinder)=PR/t where: P is the internal pressure, tis the wall thickness and R is the radius.

Still referring to the example, an exemplary geometry for the hexagonalarray 28 of internal support posts 24 is illustrated in FIG. 4. Thehexagonal array 28 includes seven internal support posts 24, six ofwhich are at the corners of the hexagon and one in the center of thehexagon. The radius of curvature R of the saddle features 38S and thedome features 38D are design variables set by the selection of thepattern and spacing of the hexagonal array 28. In this example, thehexagonal array 28 has a 1 inch spacing S between the internal supportposts 24 and a wall thickness t for the planar top side 20T of 0.035inch. The approximate radius R at the peak of each dome 42D (FIG. 3B) is1.1 inch. Modelling each dome 42D (FIG. 3B) as a sphere, at P=1 k psioperating pressure, the dome stress is: σ_(dome)=(1 k×1.10)/(2×0.035)≅16k psi. The approximate radius R at the saddle point 40S (FIG. 3A) is0.70 inch. Modelling each saddle feature 38S as a cylinder, at P=1 k psioperating pressure, the saddle stress is: σ_(saddle)=(1k×0.70)/(0.035)≅20 k psi.

Each internal support post 24 is stressed by pressure acting on thesurrounding surface area. FIG. 4 shows that the amount of area that issupported by each post is 0.866 in². In addition, each internal supportpost 24 has a 0.25 inch diameter D with a cross-sectional area of 0.049in². At P=1 k psi the stress on each internal support post 24 is:σ_(post)=pressure×(surface area−post area)/post area≅17 k psi andσ_(post)=1000×(0.866−0.049)/0.049≅17 k psi.

There is a joint 22SP (FIG. 2) where each internal support post 24 joinsthe planar top side 20T and the planar bottom side 20B. The shear stresson these joints 22SP is significant. Preferred joint designs includewelding or brazing. The designer must evaluate the shear stress on thesejoints 22SP and confirm adequate strength.

Method of Fabrication. An exemplary method of fabrication for thepressure vessel 14 is illustrated in FIGS. 5A-5D. FIG. 5A illustratesthe step of forming the frame 18 by welding or brazing the curvedsidewalls 16 using conventional techniques. In this example, the framecomprises 321 SS and has a 12″×12″ square outline. The sidewalls 16comprise half tubes having a 2.5″ diameter D. In addition, a fitting 44is attached to at least one of the sidewalls 16 as an inlet/outlet forthe pressure vessel 14. The curved sidewalls 16 can have a thickness tof 0.063″ for a 1000 psi rated stainless steel prototype. This parametercan be engineered according to the pressure requirements of the pressurevessel 14.

FIG. 5B illustrates the step of forming the planar top side 20T and theplanar bottom side 20B with contoured surfaces 36 having the shapedpressure resistant features 38. The preferred method for forming thecontoured planar surfaces 36 and the shaped pressure resistant features38 is by hydraulic pressurization (or hydroforming) of the originallyflat surfaces by in situ hydraulic pressurization of the assembledpressure vessel 14. For example, the hydraulic pressurization can beperformed along with a high pressure hydraulic fluid generated by ahydraulic pump. The hydraulic fluid causes the metal to expand.Alternately rather than being performed in situ on the assembledpressure vessel, the forming step can be accomplished using flat metalplates in the desired shapes of the planar top side 20T and the planarbottom side 2013, prior to assembly of the pressure vessel 14. In eithercase, the resulting distortion, using geological terms, forms the domefeatures 38S 38D (FIG. 3A) and the saddle features 38S (FIG. 313) in theareas between internal support posts 24 with transitions 41therebetween. The resulting short radius curved surfaces reduce hoopstress in the surface material of the contoured surface 36. Plasticstrain in forming the contoured surface 36 and the shaped pressureresistant features 38 also induces prestress or “autofrettage”. Thecomplex shapes of the contoured surface 36 and the shaped pressureresistant features 38 are naturally resistant to the internal pressureby which they were formed. As will be further explained, hydraulicinflation can also be used as controllable means of tensioningreinforcing fibers of composite pressure vessels before curing of aresin. Lastly, the dome features 38D and the saddle features 38S canhave a pattern, such as a hexagonal array, that corresponds to thepattern of the internal support posts 24.

FIG. 5C illustrates the step of forming the hexagonal array 28 ofinternal support posts 24 on the planar top side 20T and the planarbottom side 20B. This step can be performed by forming the welded orbrazed joints 22SP (FIG. 2) using conventional welding or brazingtechniques.

FIG. 5D illustrates the step of attaching the planar top side 20T andthe planar bottom side 20B to the frame 18 to form the sealed pressurechamber 26. This step can also be performed using conventional weldingor brazing techniques. As previously explained, the contoured surfaces36 and the shaped pressure resistant features 38 can be formed after theplanar top side 20T and the planar bottom side 20B have been welded tothe frame 16 using hydraulic pressurization by applying a pressure tothe sealed pressure chamber 26 that is much higher than an intendedservice pressure of the pressure vessel 10 to induce plastic strain.

Referring to FIG. 6, a composite pressure vessel 14C is illustrated. Thecomposite pressure vessel 14C uses the pressure vessel 14 as a metalliner reinforced with carbon fiber, glass fiber, fiber/epoxy tape andcured fiber/epoxy materials. The composite pressure vessel 14C includeswrapped sidewalls 16C and reinforced tubular internal support posts 24C.The composite pressure vessel 14C also includes planar top side 20TC andplanar bottom side 20BC having reinforced contoured surfaces 36C. Thecomposite pressure vessel 14C can have an increase of service pressureof about 10× over the pressure vessel 14 (FIG. 2). An exemplary increaseof service pressure can be from 1 ksi to 10 ksi. Light gases, especiallyhydrogen, permeate at significant rates through many polymeric pressurevessel materials, including polyethylene and epoxy. To avoid thisproblem, the impermeable internal pressure vessel 14 can be wrapped withhigh strength composite materials providing external support for thecomposite pressure vessel 14C.

Referring to FIG. 7, reinforcing of the composite internal support posts24C and the contoured surfaces 36C for the composite pressure vessel 14Cusing carbon fiber 46 is illustrated. In this example, 12 strands of thecarbon fiber 46 pass through each composite internal support posts 24Cper layer of wrap (e.g. 24 for 2 layers etc.) along with additionalstrands of carbon fiber 46A (see FIG. 8) for axial and radialreinforcement. The composite internal support posts 24C also providesealed passages between two or more pressure vessel surfaces throughwhich the carbon fiber 46 can be passed without concern for gaspermeation. As will be further explained, rather than using carbon fiber46 for reinforcing, a glass fiber, or a fiber/epoxy tape can beemployed. In addition, the hydraulic forming of the contoured surfaces36C after reinforcing provides a mechanism for tensioning the carbonfibers 46. In addition, the carbon fibers 46 can be coated with abinder, such as epoxy, that can be cured following tensioning.

Referring to FIG. 8, reinforcing of the sidewalls 16C using the carbonfiber 46 is illustrated. In this example, the sidewalls 16C aresemicircular and have a tube centerline substantially as shown. Inaddition, the carbon fiber 46 includes strands for axial reinforcementand can pass through the composite internal support posts 24C and acrossthe contoured surfaces 36C substantially as previously described.

Referring to FIG. 9, reinforcing of the sidewalls 16C and the internalsupport posts 24C by wrapping with fiber/epoxy tape 46T is illustrated.Wrapping with one continuous ribbon of fiber/epoxy tape 46T lends itselfto automation. In addition, multiple layers of fiber/epoxy tape 46Tprovide high strength reinforcement. Still further, wrapping with onecontinuous ribbon of fiber/epoxy tape 46T (or carbon fiber 46) permitsboth stressed planar and curved surfaces to be strengthened. Inaddition, the internal support posts 24C inside the composite pressurevessel 14C form sealed passageways for the ribbon of fiber/epoxy tape46T. In this manner gas does not contact the fiber/epoxy tape 46T andthere is no permeation.

Referring to FIG. 10, an alternate embodiment composite pressure vessel14C(PC) is illustrated. The composite pressure vessel 14C(PC) has apolygonal outline that facilitates applying of the fiber/epoxy tape 46T.For example, corners 48 of the polygonal outline of the compositepressure vessel 14C(PC) can be parallel to a row 50 of compositeinternal support posts 24C of the hexagonal array 28 substantially asshown in FIG. 10.

Referring to FIG. 11, a stress analysis of the composite internalsupport posts 24C of the hexagonal array 28 is illustrated. In FIG. 11,the composite internal support posts 24C comprise hollow metal tubesfilled with a fiber reinforcing material 46F. In addition, the fiberreinforcing material 46F is also wrapped around the contoured surfaceand the sidewalls 16C as previously explained. In this analysis, asurrounding metal surface area equals 0.866 in², a tube internal areaequals 0.0498 in², a fiber/epoxy allowable stress equals 164 k psi andthe internal pressure equals 10 k psi.

In FIG. 11:

-   -   1″ Hexagonal post array    -   10 k psi internal pressure    -   F=A×164 K psi=10 k psi×(0.866 in²−A)    -   A (1+10/164) in²=10/164 (0.866) in²    -   1.062 A in²=0.528 in²    -   A=0.0498 in²    -   Radius=0.126 in    -   ID=0.252 in    -   Tube Wall*=0.035    -   Tube OD*=0.322    -   164 k psi allowable stress*        -   *Tensile strength=370 k psi        -   *Safety factor=2.25    -   Tubes displace 9.4% of internal tank volume    -   *Neither the strength nor the unstressed area of the tube wall        were included in this analysis. These are small errors in the        interest of simplicity resulting in greater safety factor.

Referring to FIG. 12 the rectilinear box volume 50 occupied by thepressure vessel 14 (or the composite pressure vessel 14C) can becalculated as follows:

rectilinear  box  volume  50 = 10R × 10R × 2R = 200R³ $\begin{matrix}{{{center}\mspace{14mu}{section}} = {{8R \times 8R \times 2R} =}} & {128.00R^{3}} \\{{4\mspace{14mu}{sides}} = {{4 \times 0.5\pi\; R^{2} \times 8R} = {{16\pi\; R^{3}} =}}} & {50.27R^{3}} \\{{4\mspace{14mu}{corners}} = {{4 \times \frac{4}{3}R^{3}} = {{\frac{16}{3}R^{3}} =}}} & 5.33 \\\; & \overset{\_}{183.60R^{3}}\end{matrix}$ Space  Utilization  Efficiency = 183.6/200 = 91.8%

While a number of exemplary aspects and embodiments have been discussedabove, those of skill in the art will recognize certain modifications,permutations, additions and subcombinations thereof. It is thereforeintended that the following appended claims and claims hereafterintroduced are interpreted to include all such modifications,permutations, additions and sub-combinations as are within their truespirit and scope.

What is claimed is:
 1. A composite pressure vessel comprising: aplurality of curved sidewalls configured as a frame having a polygonaloutline; at least two opposing sides including a top side and a bottomside attached to the curved sidewalls forming a sealed pressure chambertherebetween configured to contain a fluid or a gas at a pressure, atleast one of the sides including a contoured surface comprising aplastically strained metal having a plurality of shaped features formedthereon configured to resist the pressure, the shaped features includingdome features and saddle features formed in the contoured surface withtransitions therebetween, each dome feature having a first cross sectioncomprising a plurality of spaced domes with a first radius, each saddlefeature having a second cross section comprising a saddle point with asecond radius; a plurality of internal support posts within the sealedpressure chamber attached to the sides in a geometrical pattern, theinternal support posts comprising hollow tubes reinforced with areinforcing material passed through the internal support posts, andtensioned on and reinforcing the contoured surface; and a plurality ofjoints between the internal support posts and the sides configured toseal an interior of each internal support post from the sealed pressurechamber and to resist shear stresses and prevent leakage or permeationof the fluid or the gas from the sealed pressure chamber at the pressureand with the interior of each internal support post forming, a sealedpassage.
 2. The composite pressure vessel of claim 1 wherein thereinforcing material comprises carbon fibers, glass fibers, fiber/epoxytape or cured fiber/epoxy materials.
 3. A composite pressure vesselcomprising: a plurality of curved sidewalls configured as a frame havinga polygonal outline; at least two opposing sides including a top sideand a bottom side attached to the curved sidewalls forming a sealedpressure chamber therebetween configured to contain a fluid or a gas ata pressure, at least one of the sides including a contoured surfacecomprising a prestressed metal having a plurality of shaped featuresformed thereon configured to resist the pressure, the shaped featuresincluding dome features and saddle features formed in the contouredsurface with transitions therebetween, each dome feature having a firstcross section comprising a plurality of spaced domes with a firstradius, each saddle feature having a second cross section comprising asaddle point with a second radius; a plurality of internal support postswithin the sealed pressure chamber attached to the sides in ageometrical pattern, the internal support posts comprising hollow tubesreinforced with a prestressed reinforcing material passed through theinternal support posts and covering the contoured surface and the curvedsidewalls; and a plurality of joints between the internal support postsand the sides configured to seal an interior of each internal supportpost from the sealed pressure chamber and to resist shear stresses andprevent leakage or permeation of the fluid or the gas from the sealedpressure chamber at the pressure and with the interior of each internalsupport post forming a sealed passage.
 4. The composite pressure vesselof claim 3 wherein the sides are parallel to one another and theinternal support posts are perpendicular to the sides.
 5. The compositepressure vessel of claim 3 wherein the polygonal outline comprises arectangle.
 6. The composite pressure vessel of claim 3 wherein thecurved sidewalls and the sides are configured as a metal liner for thereinforcing material.